An adviser to the real-estate mogul and reality TV star circulated a cryptic advisory Wednesday night that The Donald will make “a major announcement” early Thursday afternoon local time at the Trump International Hotel & Tower in Las Vegas. “The announcement will pertain to the presidential race,” Trump adviser Michael Cohen wrote in an email.

Will he run? Or will be endorse? And if he endorses, who would he pick? Mr. Trump could throw his weight behind an insurgent — Newt Gingrich or Rick Santorum. Or he could go with the establishment pick — Mitt Romney. Given his back-and-forth with Ron Paul, it seems unlikely he’d back the Texas congressman. Or maybe he, too, will sound a Herman Cain-esque endorsement of “the people.”

Mr. Trump loves to keep people guessing — and elbowing his way into the headlines. Perhaps the best question, if he’s not throwing his hat in the ring, is whether the candidate who receives his endorsement actually wants his backing.

“I have no idea what The Donald is going to do,” Mr. Gingrich said. “He is always interesting, and I don’t know of anybody who does a better job of getting attention by announcing that he will presently announce something.”